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2011 Super Outbreak
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2011 Super Outbreak
The 2011 Super Outbreak was the largest and costliest tornado outbreak ever recorded, taking place in the Southern, Midwestern, and Northeastern United States from April 25 to 28, 2011, leaving catastrophic destruction in its wake. Over 175 tornadoes struck Alabama, Mississippi, and Tennessee, which were the most severely damaged states. Other destructive tornadoes occurred in Arkansas, Georgia, Kentucky, Louisiana, New York, and Virginia, with storms also affecting other states in the Southern and Eastern United States. In total, 368 tornadoes were confirmed by NOAA's National Weather Service (NWS) and Government of Canada's Environment Canada in 21 states from Texas to New York to southern Canada. Widespread and destructive tornadoes occurred on each day of the outbreak. April 27 was the most active day, with a record 224 tornadoes touching down that day from midnight to midnight CDT (05:00–05:00 UTC). Four of the tornadoes were rated EF5, which is the highest ranking on the Enhanced Fujita scale; typically these tornadoes are recorded no more than once a year.
In total, 348 people were killed as a result of the outbreak, including 324 tornado-related deaths across six states and 24 fatalities caused by other thunderstorm-related events such as straight-line winds, hail, flash flooding or lightning. In Alabama alone, 238 tornado-related deaths were confirmed by the Storm Prediction Center (SPC) and the state's Emergency Management Agency. April 27's 316 fatalities were the most tornado-related fatalities in the United States in a single day since the "Tri-State" outbreak on March 18, 1925 (when at least 751 people were killed). Nearly 500 preliminary local storm reports were received for tornadoes over four days, including 292 in 16 states on April 27 alone. This event was the costliest tornado outbreak in United States history, with total damage reaching $10.2 billion (equivalent to $15 billion in 2025). In 2023, tornado expert Thomas P. Grazulis created the outbreak intensity score (OIS) as a way to rank various tornado outbreaks. The 2011 Super Outbreak received an OIS of 383, making it the second most intense tornado outbreak in recorded history behind only the 1974 Super Outbreak.
The outbreak was caused by a vigorous upper-level trough that moved into the Southern Plains states on April 25. An extratropical cyclone developed ahead of this upper-level trough between northeastern Oklahoma and western Missouri, and moved northeastward. Conditions were similar on April 26, with a predicted likelihood of severe thunderstorms, including an extended threat of strong to violent long-track tornadoes throughout the afternoon and evening; mixed-layer CAPE values were forecast to be around 3000–4000 J/kg, around east Texas, Louisiana, and Arkansas. The storm mode on April 26 was predicted to include mostly discrete tornadic supercells during both the afternoon and the early evening, shifting over to a mesoscale convective complex, with more of a threat of damaging winds and hail during the nighttime.
As the storm system moved eastward toward the Ohio, Mississippi, and Tennessee Valleys on April 27, a very powerful 80–100 knot mid-level jet stream moved into the Ohio and Tennessee Valleys behind the trough and created strong wind shear, along with a low pressure center moving quickly northeastward across those areas on April 27. During the afternoon of April 27, CAPE values were estimated to be in the range of 2000–3000 J/kg across Louisiana and southern Mississippi, with the moderate instability moving northeastward across the southern Tennessee Valley; additionally, temperatures across the southeastern United States ranged from the 70s °F (mid-20s °C) to the lower 90s °F (near 35 °C). Helicity levels ranged from 450 to 600 m2/s2, which supported some significant tornadic activity and strong to violent long-track tornadoes. At 06:10 UTC, the SPC issued a second-consecutive, high risk day-one outlook, featuring a 30% hatched risk of tornadoes centered over northern Alabama. At 16:30 UTC (11:30 AM CDT) this region was expanded to include portions of eastern Mississippi, southern Tennessee, and northwest Georgia. Additionally, a rare, 45% hatched risk of tornadoes was introduced along a corridor from Meridian, Mississippi, to Huntsville, Alabama.
A total of 56 severe weather watches were issued by the Storm Prediction Center (SPC) over those four days in the outbreak area. This included 41 tornado watches—10 of which were particularly dangerous situation (PDS) watches—and 15 severe thunderstorm watches. The SPC assigns numbers to each severe weather watch issued starting at the beginning of each year; the organization unsuccessfully used two of their allocated watch numbers during this outbreak (numbers 208 and 209). The Storm Prediction Center received 292 reports of tornadoes in the preceding 24 hours. In addition to setting the record for most tornadoes in a calendar day (223; midnight to midnight CDT (05:00 – 05:00 UTC)), it also broke the record for the most tornado touchdowns in any 24-hour period with 226 from 12:40 a.m. to 12:40 a.m. CDT (05:40 – 05:40 UTC) April 27–28, breaking the old 24-hour record of 148 set by the 1974 Super Outbreak. Of those 226 tornadoes, 59 touched down in Alabama and 83 began in Tennessee, accounting for 62.8 percent of the tornadoes that touched down on April 27. On April 27 alone, the National Weather Service in Huntsville, Alabama, issued 92 tornado warnings, 31 severe thunderstorm warnings, and seven flash flood warnings. The National Weather Service in Birmingham, Alabama issued 49 tornado warnings, and 24 severe thunderstorm warnings. In total, 449 tornado warnings were issued on April 27
* One tornado touched down in Ontario, Canada, on April 27 and was rated as an F0. It is counted as an EF0 in this table.
A record 368 tornadoes touched down over the span of four days, 37 of which were EF3+ tornadoes. Four tornadoes were rated EF5 – behind only the 1974 Super Outbreak (7 F5s). Several of the strong to violent tornadoes that formed were exceptionally long-tracked, with six tornadoes on April 27 tracking over 60 miles (97 km). Many tornadoes on the afternoon of April 27 were spawned from a collection of supercells that moved across Mississippi, Alabama, Tennessee, and Georgia.
The period from 2:28 p.m. CDT (1928 UTC) to 9:10 p.m. CDT (0210 UTC) represented nearly seven hours of continuous tornado activity during the height of the outbreak of April 27, during which 94 tornadoes touched down. All fifteen violent EF4+ tornadoes occurred continuously during this time, beginning with the Philadelphia, Mississippi EF5 tornado at 2:30 p.m. CDT (1930 UTC) and concluding with the dissipation of the Lake Martin/Dadeville EF4 tornado at 9:09 p.m. CDT (0209 UTC). Several tornadoes from the outbreak were exceptionally long-tracked. Three tornadoes on April 27 travelled over 120 miles (190 km), with a fourth traversing 97 miles (156 km). Seven tornadoes–the Vilonia tornado on April 25 and six tornadoes on April 27–stayed on the ground for over an hour. The long-track Mississppi-Alabama EF4 was down from 2 hours, 53 minutes, the longest duration for a tornado in the outbreak.
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2011 Super Outbreak
The 2011 Super Outbreak was the largest and costliest tornado outbreak ever recorded, taking place in the Southern, Midwestern, and Northeastern United States from April 25 to 28, 2011, leaving catastrophic destruction in its wake. Over 175 tornadoes struck Alabama, Mississippi, and Tennessee, which were the most severely damaged states. Other destructive tornadoes occurred in Arkansas, Georgia, Kentucky, Louisiana, New York, and Virginia, with storms also affecting other states in the Southern and Eastern United States. In total, 368 tornadoes were confirmed by NOAA's National Weather Service (NWS) and Government of Canada's Environment Canada in 21 states from Texas to New York to southern Canada. Widespread and destructive tornadoes occurred on each day of the outbreak. April 27 was the most active day, with a record 224 tornadoes touching down that day from midnight to midnight CDT (05:00–05:00 UTC). Four of the tornadoes were rated EF5, which is the highest ranking on the Enhanced Fujita scale; typically these tornadoes are recorded no more than once a year.
In total, 348 people were killed as a result of the outbreak, including 324 tornado-related deaths across six states and 24 fatalities caused by other thunderstorm-related events such as straight-line winds, hail, flash flooding or lightning. In Alabama alone, 238 tornado-related deaths were confirmed by the Storm Prediction Center (SPC) and the state's Emergency Management Agency. April 27's 316 fatalities were the most tornado-related fatalities in the United States in a single day since the "Tri-State" outbreak on March 18, 1925 (when at least 751 people were killed). Nearly 500 preliminary local storm reports were received for tornadoes over four days, including 292 in 16 states on April 27 alone. This event was the costliest tornado outbreak in United States history, with total damage reaching $10.2 billion (equivalent to $15 billion in 2025). In 2023, tornado expert Thomas P. Grazulis created the outbreak intensity score (OIS) as a way to rank various tornado outbreaks. The 2011 Super Outbreak received an OIS of 383, making it the second most intense tornado outbreak in recorded history behind only the 1974 Super Outbreak.
The outbreak was caused by a vigorous upper-level trough that moved into the Southern Plains states on April 25. An extratropical cyclone developed ahead of this upper-level trough between northeastern Oklahoma and western Missouri, and moved northeastward. Conditions were similar on April 26, with a predicted likelihood of severe thunderstorms, including an extended threat of strong to violent long-track tornadoes throughout the afternoon and evening; mixed-layer CAPE values were forecast to be around 3000–4000 J/kg, around east Texas, Louisiana, and Arkansas. The storm mode on April 26 was predicted to include mostly discrete tornadic supercells during both the afternoon and the early evening, shifting over to a mesoscale convective complex, with more of a threat of damaging winds and hail during the nighttime.
As the storm system moved eastward toward the Ohio, Mississippi, and Tennessee Valleys on April 27, a very powerful 80–100 knot mid-level jet stream moved into the Ohio and Tennessee Valleys behind the trough and created strong wind shear, along with a low pressure center moving quickly northeastward across those areas on April 27. During the afternoon of April 27, CAPE values were estimated to be in the range of 2000–3000 J/kg across Louisiana and southern Mississippi, with the moderate instability moving northeastward across the southern Tennessee Valley; additionally, temperatures across the southeastern United States ranged from the 70s °F (mid-20s °C) to the lower 90s °F (near 35 °C). Helicity levels ranged from 450 to 600 m2/s2, which supported some significant tornadic activity and strong to violent long-track tornadoes. At 06:10 UTC, the SPC issued a second-consecutive, high risk day-one outlook, featuring a 30% hatched risk of tornadoes centered over northern Alabama. At 16:30 UTC (11:30 AM CDT) this region was expanded to include portions of eastern Mississippi, southern Tennessee, and northwest Georgia. Additionally, a rare, 45% hatched risk of tornadoes was introduced along a corridor from Meridian, Mississippi, to Huntsville, Alabama.
A total of 56 severe weather watches were issued by the Storm Prediction Center (SPC) over those four days in the outbreak area. This included 41 tornado watches—10 of which were particularly dangerous situation (PDS) watches—and 15 severe thunderstorm watches. The SPC assigns numbers to each severe weather watch issued starting at the beginning of each year; the organization unsuccessfully used two of their allocated watch numbers during this outbreak (numbers 208 and 209). The Storm Prediction Center received 292 reports of tornadoes in the preceding 24 hours. In addition to setting the record for most tornadoes in a calendar day (223; midnight to midnight CDT (05:00 – 05:00 UTC)), it also broke the record for the most tornado touchdowns in any 24-hour period with 226 from 12:40 a.m. to 12:40 a.m. CDT (05:40 – 05:40 UTC) April 27–28, breaking the old 24-hour record of 148 set by the 1974 Super Outbreak. Of those 226 tornadoes, 59 touched down in Alabama and 83 began in Tennessee, accounting for 62.8 percent of the tornadoes that touched down on April 27. On April 27 alone, the National Weather Service in Huntsville, Alabama, issued 92 tornado warnings, 31 severe thunderstorm warnings, and seven flash flood warnings. The National Weather Service in Birmingham, Alabama issued 49 tornado warnings, and 24 severe thunderstorm warnings. In total, 449 tornado warnings were issued on April 27
* One tornado touched down in Ontario, Canada, on April 27 and was rated as an F0. It is counted as an EF0 in this table.
A record 368 tornadoes touched down over the span of four days, 37 of which were EF3+ tornadoes. Four tornadoes were rated EF5 – behind only the 1974 Super Outbreak (7 F5s). Several of the strong to violent tornadoes that formed were exceptionally long-tracked, with six tornadoes on April 27 tracking over 60 miles (97 km). Many tornadoes on the afternoon of April 27 were spawned from a collection of supercells that moved across Mississippi, Alabama, Tennessee, and Georgia.
The period from 2:28 p.m. CDT (1928 UTC) to 9:10 p.m. CDT (0210 UTC) represented nearly seven hours of continuous tornado activity during the height of the outbreak of April 27, during which 94 tornadoes touched down. All fifteen violent EF4+ tornadoes occurred continuously during this time, beginning with the Philadelphia, Mississippi EF5 tornado at 2:30 p.m. CDT (1930 UTC) and concluding with the dissipation of the Lake Martin/Dadeville EF4 tornado at 9:09 p.m. CDT (0209 UTC). Several tornadoes from the outbreak were exceptionally long-tracked. Three tornadoes on April 27 travelled over 120 miles (190 km), with a fourth traversing 97 miles (156 km). Seven tornadoes–the Vilonia tornado on April 25 and six tornadoes on April 27–stayed on the ground for over an hour. The long-track Mississppi-Alabama EF4 was down from 2 hours, 53 minutes, the longest duration for a tornado in the outbreak.
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